This invention relates to silicon carbide based monoliths and, more particularly, it concerns a lime-free silicon carbide refractory which can be used in various non-ferrous applications, such as aluminum production, ferroalloy production, tin production, copper production, and also as a refractory covering for boiler tubes.
It is recognized that the highest wear and maintenance area in an aluminum reverberatory furnace is the belly band area. This area comprises the fluctuating zone between molten metal and air. The belly band zone is subjected to corundum (Al.sub.2 O.sub.3) buildup. (due to oxidation of the metal), reactions between the refractory and the molten metal, reactions between the refractory and cover fluxes on the molten metal, mechanical scrapping to remove the tough corundum buildup, and high combustion temperatures since a gas flame is directed onto the surface of the molten bath. As the belly band area becomes worn or eroded, the upper sidewall of the furnace becomes undercut and hence becomes unstable. This necessitates bringing the furnace off line and repairing the belly band. Current refractory materials used to line the belly band are phosphate bonded high alumina brick and monoliths as well as zircon brick. Although these materials perform reasonably well, localized wear at the belly band is a problem. Hence, there is an ongoing need for a more durable and stable belly band refractory.
Ferroalloys, such as 75 wt.% Si/25 wt.%Fe are typically formed in submerged arc furnaces. In such a furnace, the temperature of the molten ferroalloy is very high, typically near 3200-3300.degree. F. The molten alloys are tapped from the furnace and poured through troughs into receiving ingots. The troughs are typically made from cement bonded 60 wt.% SiC/alumina castables. The castables are typically cast into rectangular shapes about 37.times.175/8.times.6". Carbon paste is then rammed over the rectangular shapes to form a trough-shaped configuration. These carbon troughs protect the blocks from the effects of the initial heat. Even though this carbon trough lining material works reasonably well, a more durable and stable refractory is desired.
In waste-to-energy incinerators, boiler tubes filled with cooling water are used to transfer heat from the confines of the incinerator. Boiler tubes are used to construct the walls of the combustion chamber in the incinerator. Because the boiler tubes cannot withstand direct contact with the high temperatures in the interior of the incinerator, they are lined with a high conductivity refractory. Historically, silicon carbide-based refractories have been used for this purpose. These refractories have been bonded with silicates, phosphates, or calcium aluminate cements. While surface life has been adequate, a longer refractory life of the boiler tube lining is desired.